Transmission mechanism of image scanner with adjustable resolution

ABSTRACT

A transmission mechanism of an image scanner with adjustable resolution is disclosed. The transmission device is driven by a step motor to move a carriage to perform a scanning operation at a selected speed The transmission device includes a transmission control set switched between a first and a second transmission states in response to a command for changing a moving speed of the carriage, and driven by the step motor to output a transmission power; a first transmission set of a first deceleration ratio, coupled with the transmission control set to receive the transmission power from the transmission control set in the first transmission state, and providing the transmission power for the carriage to have the carriage move at a first speed; and a second transmission set of a second deceleration ratio different from the first deceleration ratio, coupled with the transmission control set to receive the transmission power from the transmission control set in the second transmission state, and providing the transmission power for the carriage to have the carriage move at a second speed.

FIELD OF THE INVENTION

The present invention relates to a transmission mechanism of an imagescanner, and more particularly to a transmission mechanism of an imagescanner with adjustable resolution.

BACKGROUND OF THE INVENTION

Nowadays, image scanners have become common peripheral equipment ofcomputers. As known, resolution of an image scanner is one of theimportant indices to evaluate a scanner. In general, resolution consistsof two components, i.e. horizontal resolution and vertical resolution.The horizontal resolution depends on the specification of the opticalsystem, the pixel number of the image pickup device such as acharge-coupled device (CCD) and/or hardware circuitry. The verticalresolution, on the other hand, relates to the operations of thetransmission device 11 and step motor 12 shown in FIG. 1.

An advanced image scanner provides two options for users. The imagescanner may perform a scanning operation on the conditions of arelatively high speed but relatively low resolution. Alternatively, thescanning operation may be performed on the conditions of a relativelyhigh resolution but a relatively low speed. The prior art techniqueadjusts the scanning resolution and speed by changing the revolvingspeed of the step motor. However, the motor at a high revolving speedgenerates significant noise, and is required to be a high torque motorthat is of high cost and bulky.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide atransmission mechanism of an image scanner, which facilitates theresolution of the image scanner to be adjusted without changing therevolving speed of the step motor.

A first aspect of the present invention relates to a transmission devicefor use in an image scanner. The transmission device is driven by a stepmotor to move a carriage to perform a scanning operation at a selectedspeed, and includes a transmission control set switched between a firstand a second transmission states in response to a command for changing amoving speed of the carriage, and driven by the step motor to output atransmission power; a first transmission set of a first decelerationratio, coupled with the transmission control set to receive thetransmission power from the transmission control set in the firsttransmission state, and providing the transmission power for thecarriage to have the carriage move at a first speed; and a secondtransmission set of a second deceleration ratio different from the firstdeceleration ratio, coupled with the transmission control set to receivethe transmission power from the transmission control set in the secondtransmission state, and providing the transmission power for thecarriage to have the carriage move at a second speed.

In an embodiment, the transmission control set includes an active gearsynchronously rotating with a shaft of the step motor; two followergears engaging with the active gear to be transmitted by the activegear; and a swing arm connecting the two follower gears with each other,and swinging between a first position to allow the follower gears toengage with the first transmission set and a second position to allowthe follower gears to engage with the second transmission set. The swingarm swings to the first position in response to a first rotatingdirection of the shaft of the step motor, and swings to the secondposition in response to a second rotating direction of the shaftopposite to the first rotating direction.

Preferably, the transmission control set further includes a holderoptionally holding the swing arm to fix a configuration of thetransmission device to allow the carriage to move at the selected speed;and an electromagnetic valve coupled with the holder for retracting theholder to release the swing arm in order to change the moving speed ofthe carriage, and protracting the holder to confine the swing arm inorder to fix the configuration of the transmission device for thescanning operation. The holder is connected to one end of a spring whichis fixed at the other end thereof, and the spring stretches when theelectromagnetic valve is activated to retract the holder, and recoversto protract the holder when the electromagnetic valve is deactivated.

Preferably, the first and second transmission devices are a first and asecond gear sets, respectively, and the first and second gears setsinclude a common gear that moves the carriage via a cyclic belt.

A second aspect of the present invention relates to a transmissiondevice for use in an image scanner which is driven by a step motor tomove an image pickup device relative to a scanned object via a movingelement to perform a scanning operation at a selected speed. Thetransmission device includes a state controller for determining atransmission state of the transmission device according to the selectedspeed; a first gear set of a first deceleration ratio, connected betweenthe step motor and the moving element to move the image pickup devicerelative to the scanned document at a first speed in a firsttransmission state; and a second gear set of a second deceleration ratiowhich differs from the first deceleration ratio, connected between thestep motor and the moving element to move the image pickup devicerelative to the scanned object at a second speed in a secondtransmission state.

In an embodiment, the state controller includes an active gear coupledand synchronously rotating with a shaft of the step motor; two followergears engaging with the active gear to be transmitted by the activegear; and a swing arm connecting the two follower gears with each other,and swinging between a first position to allow the first gear set toengage with the follower gears to be connected to the step motor and asecond position to allow the second gear set to engage with the followergears to be connected to the step motor. The swing arm swings to thefirst position in response to a first rotating direction of the shaft ofthe step motor, and swings to the second position in response to asecond rotating direction of the shaft opposite to the first rotatingdirection.

Preferably, the moving element includes a cyclic belt for moving theimage pickup device in a flatbed scanner. In an auto-feeding scanner, onthe other hand, includes a roller for moving the scanned object.

A third aspect of the present invention relates to an image scanner withadjustable resolution. The image scanner includes an image pickup devicefor converting an image of a scanned object into digital data; a stepmotor providing a moving power for a relative movement of the imagepickup device to the scanned object to complete scanning; a first gearset driven by the step motor to transmit the moving power, and switchedto either of a first and a second positions for adjusting resolution; asecond gear set of a first deceleration ratio, located at a positioncorresponding to the first position of the first gear set for optionallyengaging with the first gear set so as to receive and further transmitthe moving power in a first manner; a third gear set of a seconddeceleration ratio, located at a position corresponding to the secondposition of the first gear set for optionally engaging with the firstgear set to further transmit the moving power in a second manner; and amoving element coupled with both of the second and third gear sets, andreceiving the moving power from the one of the second and third sets,which engages with the first gear set, to move the image pickup devicerelative to the scanned object at a selected speed, thereby adjustingresolution of the image scanner.

Preferably, the first gear set includes an active gear coupled andsynchronously rotating with a shaft of the step motor; two followergears engaging with the active gear to be transmitted by the activegear; and a swing arm connecting the two follower gears with each other,and swinging between the first position to allow the second gear set toengage with the follower gears and the second position to allow thethird gear set to engage with the follower gears.

Preferably, the image scanner further includes a holder optionallyholding the swing arm to fix a configuration of the first, second andthird gear sets to allow the moving power to be transmitted in a certainone of the first and second manners; and an electromagnetic valvecoupled with the holder for retracting the holder to release the swingarm for resolution adjustment, and protracting the holder to confine theswing arm for scanning operation. The holder is connected to one end ofa spring which is fixed at the other end thereof, and the springstretches when the electromagnetic valve is activated to retract theholder, and recovers to protract the holder when the electromagneticvalve is deactivated.

The image scanner can be a flatbed scanner, and the moving elementincludes an end gear engaging with both of the second and third gearsets; and a cyclic belt transmitted by the end gear to move the imagepickup device.

The image scanner can also be an auto-feeding scanner, and the movingelement includes an end gear engaging with both of the second and thirdgear sets; and a roller synchronously rotating with the end gear to feedthe scanned object.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may best be understood through the followingdescription with reference to the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional side view of a conventionalflatbed scanner;

FIGS. 2A˜2D are schematic diagrams showing the operations of a preferredembodiment of a transmission device according to the present invention;

FIGS. 3A and 3B are schematic diagrams showing the optional powertransmission paths of the transmission device of FIG. 2; and

FIGS. 4A and 4B are schematic diagrams illustrating the application ofthe transmission device of FIG. 2 to a flatbed scanner and anauto-feeding scanner, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described more specifically withreference to the following embodiments. It is to be noted that thefollowing descriptions of preferred embodiments of this invention arepresented herein for purpose of illustration and description only; it isnot intended to be exhaustive or to be limited to the precise formdisclosed.

Please refer to FIGS. 2A˜2D which illustrate a preferred embodiment of atransmission device according to the present invention used in a flatbedscanner similar to that shown in FIG. 1. The transmission deviceincludes an electromagnetic valve 20 with a rod 201, a holder 21, astretch spring 22, a control gear set 23, a first and a secondtransmission gear sets 24 and 25, and a common transmission gear 26. Thecontrol gear set 23 includes an active gear 231 concentrically coupledand synchronously rotating with the shaft 271 of a step motor 27, andtwo follower gears 232 and 233 which are combined together with a swingarm 234. The swing arm 234 has a protruding end 235 heading toward theholder 21. The follower gears 232 and 233 optionally engage with eitherof the transmission gear sets 24 and 25. The common gear set 26 engageswith both of the transmission gear sets 24 and 25, and is sleevedtherearound a cyclic belt 40, as shown in FIG. 4A, for moving a carriage41 installed therein an image pickup device such as a charge-coupleddevice (CCD) or a contact image sensor (CIS).

Before a scanning operation is performed, the user may give a commandfor example via a switch mounted on the scanner housing (not shown) todetermine the desired resolution. When a relatively high resolution isrequired, the scanning speed should be lowered. Therefore, atransmission mechanism of a high deceleration ratio is selected to forpower transmission. In this embodiment, the first transmission gear set24 has a relatively high deceleration ratio so as to be suitable forrelatively high resolution scanning. On the contrary, when a relativelyhigh scanning speed is required under sacrificed resolution, atransmission mechanism of a low deceleration ratio is selected to forpower transmission. In this embodiment, the second transmission gear set25 has a relatively low deceleration ratio so as to be suitable forrelatively low resolution scanning. Hereinafter, the high-low resolutionswitching operation and the scanning operation performed under theselected speed and resolution will be described with reference to FIGS.2A˜2D and 3A˜3B.

FIG. 2A schematically shows that the image scanner performs a highresolution but low speed scanning operation. The follower gears 232 and233 of the control gear set 23 are made to engage with the first gearset 24 by confining by the holder 21 at a position A. Then the shaft 271of the step motor 27 rotates in a certain direction, for examplecounterclockwise, to drive the present transmission device via thetransmission path shown in FIG. 3A to transmit the cyclic belt 40,thereby moving the carriage 41 forwards to scan an object to be scanned.When the scanning operation is finished, the shaft 271 rotates in anopposite direction, for example clockwise, to move the carriage 41 backvia the same transmission path.

When the scanning operation is desired to be changed to a high scanningspeed but low resolution one, the protruding end 235 of the swing arm234 should be released from the holder 21 first by supplying electricityto the electromagnetic valve 20. The electric-magnetic conversionretracts the rod 201 and thus the holder 21 due to the magneticallyattractive force to release the arm 234, as shown in FIG. 2B. Meanwhile,the shaft 271 of the step motor 27 rotates clockwise to have thefollower gears 232 and 233 engage with the second transmission gear set25 so as to change the transmission path to the one shown in FIG. 3B. Atthis time, the spring 22 stretches under an unstable state due to theretraction of the rod 201 and the holder 21. After the abovetransmission-path switching operation is completed, the electricitysupply to the electromagnetic valve 20 is interrupted. Therefore, theretracting force of the electromagnetic valve 20 working on the rod 201is retreated, and the spring 22 recovers to its stable state and allowsthe rod 201 to be protracted from the electromagnetic valve 20. Theholder 21 then confines the arm 234 at the position B, referring to FIG.2C. Then the shaft 271 of the step motor 27 rotates in a certaindirection, for example counterclockwise, to drive the presenttransmission device via the transmission path shown in FIG. 3B totransmit the cyclic belt 40, thereby moving the carriage 41 forwards toscan an object to be scanned. When the scanning operation is finished,the shaft 271 rotates in an opposite direction, for example clockwise,to move the carriage 41 back via the same transmission path.

When the scanning operation is desired to be changed to a high scanningresolution but low speed one, the protruding end 235 of the swing arm234 should be released from the holder 21 again by supplying electricityto the electromagnetic valve 20. The electric-magnetic conversionretracts the rod 201 and thus the holder 21 due to the magneticallyattractive force to release the arm 234, as shown in FIG. 2D. Meanwhile,the shaft 271 of the step motor 27 is made to rotate counterclockwise tohave the follower gears 232 and 233 engage with the first transmissiongear set 24 so as to change the transmission path to the one shown inFIG. 3A. After the above transmission-path switching operation iscompleted, the electricity supply to the electromagnetic valve 20 isinterrupted, and the holder 21 confines the arm 234 at the position Aagain. Under this circumstance, the moving back and forth operation ofthe carriage can be performed in an above-mentioned manner.

It is to be noted that the transmission device illustrated in the aboveembodiment is used in a flatbed scanner for moving a carriage, as shownin FIG. 4A. The transmission device according to the present invention,however, can also be used in an auto-feeding scanner to rotate a roller42 for feeding a document, as shown in FIG. 4B.

By using the present transmission device in an image scanner or anyother scanning device requiring multi-level transmission speedadjustment, the transmission speed and thus the resolution can be easilyadjusted without raising the torque of the motor. The image scanneraccording to the present invention is thus quiet and cost-efficiently.

While the invention has been described in terms of what are presentlyconsidered to be the most practical and preferred embodiments, it is tobe understood that the invention need not be limited to the disclosedembodiment. On the contrary, it is intended to cover variousmodifications and similar arrangements included within the spirit andscope of the appended claims which are to be accorded with the broadestinterpretation so as to encompass all such modifications and similarstructures.

1. A transmission device for use in an image scanner, driven by a stepmotor to move a carriage to perform a scanning operation at a selectedspeed, and comprising: a transmission control set switched between afirst and a second transmission states in response to a command forchanging a moving speed of said carriage, and driven by said step motorto output a transmission power; a first transmission set of a firstdeceleration ratio, coupled with said transmission control set toreceive said transmission power from said transmission control set insaid first transmission state, and providing said transmission power forsaid carriage to have said carriage move at a first speed; and a secondtransmission set of a second deceleration ratio different from saidfirst deceleration ratio, coupled with said transmission control set toreceive said transmission power from said transmission control set insaid second transmission state, and providing said transmission powerfor said carriage to have said carriage move at a second speed; whereinsaid transmission control set comprises: an active gear synchronouslyrotating with a shaft of said step motor; two follower gears engagingwith said active gear to be transmitted by said active gear; and a swingarm connecting said two follower gears with each other, and swingingbetween a first position to allow said follower gears to engage withsaid first transmission set and a second position to allow said followergears to engage with said second transmission set.
 2. The transmissiondevice according to claim 1 wherein said swing arm swings to said firstposition in response to a first rotating direction of said shaft of saidstep motor, and swings to said second position in response to a secondrotating direction of said shaft opposite to said first rotatingdirection.
 3. The transmission device according to claim 2 wherein saidtransmission control set further includes: a holder optionally holdingsaid swing arm to fix a configuration of said transmission device toallow said carriage to move at said selected speed; and anelectromagnetic valve coupled with said holder for retracting saidholder to release said swing arm in order to change said moving speed ofsaid carriage, and protracting said holder to confine said swing arm inorder to fix said configuration of said transmission device for saidscanning operation.
 4. The transmission device according to claim 3wherein said holder is connected to one end of a spring which is fixedat the other end thereof, and said spring stretches when saidelectromagnetic valve is activated to refract said holder, and recoversto protract said holder when said electromagnetic valve is deactivated.5. The transmission device according to claim 1 wherein said first andsecond transmission devices are a first and a second gear sets,respectively.
 6. The transmission device according to claim 5 whereinsaid first and second gears sets include a common gear that moves saidcarriage via a cyclic belt.
 7. A transmission device for use in an imagescanner, driven by a step motor to move an image pickup device relativeto a scanned object via a moving element to perform a scanning operationat a selected speed, and comprising: a state controller for determininga transmission state of said transmission device according to saidselected speed; a first gear set of a first deceleration ratio,connected between said step motor and said moving element to move saidimage pickup device relative to said scanned document at a first speedin a first transmission state; and a second gear set of a seconddeceleration ratio which differs from said first deceleration ratio,connected between said step motor and said moving element to move saidimage pickup device relative to said scanned object at a second speed ina second transmission state; wherein said state controller includes: anactive gear coupled and synchronously rotating with a shaft of said stepmotor; two follower gears engaging with said active gear to betransmitted by said active gear; and a swing arm connecting said twofollower gears with each other, and swinging between a first position toallow said first gear set to engage with said follower gears to beconnected to said step motor and a second position to allow said secondgear set to engage with said follower gears to be connected to said stepmotor.
 8. The transmission device according to claim 7 wherein saidswing arm swings to said first position in response to a first rotatingdirection of said shaft of said step motor, and swings to said secondposition in response to a second rotating direction of said shaftopposite to said first rotating direction.
 9. The transmission deviceaccording to claim 7 wherein said first and second gears sets include acommon gear connected to said moving element which includes a cyclicbelt for moving said image pickup device.
 10. The transmission deviceaccording to claim 7 wherein said first and second gears sets include acommon gear connected to said moving element which includes a roller formoving said scanned object.
 11. An image scanner with adjustableresolution, comprising: an image pickup device for converting an imageof a scanned object into digital data; a step motor providing a movingpower for a relative movement of said image pickup device to saidscanned object to complete scanning; a first gear set driven by saidstep motor to transmit said moving power, and switched to either of afirst and a second positions for adjusting resolution; a second gear setof a first deceleration ratio, located at a position corresponding tosaid first position of said first gear set for optionally engaging withsaid first gear set so as to receive and further transmit said movingpower in a first manner; a third gear set of a second decelerationratio, located at a position corresponding to said second position ofsaid first gear set for optionally engaging with said first gear set tofurther transmit said moving power in a second manner; and a movingelement coupled with both of said second and third gear sets, andreceiving said moving power from the one of said second and third sets,which engages with said first gear set, to move said image pickup devicerelative to said scanned object at a selected speed, thereby adjustingresolution of said image scanner; wherein said first gear set includes:an active gear coupled and synchronously rotating with a shaft of saidstep motor; two follower gears engaging with said active gear to betransmitted by said active gear; and a swing arm connecting said twofollower gears with each other, and swinging between said first positionto allow said second gear set to engage with said follower gears andsaid second position to allow said third gear set to engage with saidfollower gears.
 12. The image scanner according to claim 11 furthercomprising: a holder optionally holding said swing arm to fix aconfiguration of said first, second and third gear sets to allow saidmoving power to be transmitted in a certain one of said first and secondmanners; and an electromagnetic valve coupled with said holder forretracting said holder to release said swing arm for resolutionadjustment, and protracting said holder to confine said swing arm forscanning operation.
 13. The image scanner according to claim 12 whereinsaid holder is connected to one end of a spring which is fixed at theother end thereof, and said spring stretches when said electromagneticvalve is activated to retract said holder, and recovers to protract saidholder when said electromagnetic valve is deactivated.
 14. The imagescanner according to claim 11 wherein said image scanner is a flatbedscanner, and said moving element includes: an end gear engaging withboth of said second and third gear sets; and a cyclic belt transmittedby said end gear to move said image pickup device.
 15. The image scanneraccording to claim 11 wherein said image scanner is an auto-feedingscanner, and said moving element includes: an end gear engaging withboth of said second and third gear sets; and a roller synchronouslyrotating with said end gear to feed said scanned object.